In aerospace applications, there is a constant need for exchanging heat between two flowing fluids for a variety of needs, such as lubricant fluids, pump fluids, fuel fluids and the like. Often, one fluid is used to cool another. For instance, should a coolant be used to cool various components of an aircraft, fuel might be used to exchange heat with the coolant and thereby have a self-contained or on-board heat exchange circuit. Many heat exchangers used for such purposes are quite cumbersome in a field where size and weight are critical parameters.
In aircraft and aerospace environments, one of the most readily available heat sinks that could be used as a heat exchanger medium is the air itself. However, air has poor heat transfer coefficients when compared with liquids, such as fuel, hydraulic liquid or the like, and relatively large heat exchanger structures would be required if using an air heat exchange medium. Therefore, air substantially has been dismissed as a cooling medium because of the critical size and weight limitations in aircraft applications.
The need for and the advantages of providing a gas or air/liquid heat exchanger are obvious, if the problem of designing a small, lightweight heat exchanger structure could be met.
Heat exchangers using an impingement cooling principal are known for exchanging heat between different liquids flowing through the exchanger. Some heat exchangers that use the impingement cooling principal are of the impingement plate type. With such heat exchangers, liquid passes through a plurality of holes in a given plate and strikes a solid portion or "impinges" against a subsequent, usually parallel, plate where it moves along that plate to the nearest orifice and passes through the plate for impinging against a solid portion of the next plate. Eventually, after passing through a series of plates, the liquid leaves the heat exchanger. This impingement cooling principle aids in the heat transfer between the liquid and each plate. Of course, the holes or orifices in adjacent plates are misaligned intentionally so that the liquid must impinge against a subsequent plate prior to passing through the orifices thereof. This forces the liquid to impinge against each plate after passing through the previous plate to provide a tortuous path for the liquid rather than permitting the liquid merely to flow through holes in the stack of plates.
An example of an impingement cooling apparatus employing impingement orifice plates is shown in my U.S. Pat. No. 4,494,171, dated Jan. 15, 1985, and assigned to the assignee of this invention.
Most such impingement plate type heat exchangers are designed to exchange heat between liquids which are generally similar. However, this invention is directed to providing an improved impingement plate type heat exchanger using gas (air) as a cooling medium and thereby solving the problem of using that medium in heat exchanger applications in aircraft and aerospace environments where size and weight are critical parameters.